The ability to map cerebral metabolic activity is important for diagnosis and therapy monitoring of numerous neurological disorders, including but not limited to Alzheimer's disease and other senile dementias, Huntington's disease, Parkinson's disease, multiple sclerosis, and brain tumors. Cerebral metabolic imaging typically requires the administration of a radio labeled sugar analog which is invasive and limits the spatial resolution attainable.
Metabolic imaging can be defined as mapping the distributions of metabolic molecule tissue concentrations (“levels”) and/or metabolic fluxes: the metabolic thermodynamic and kinetic aspects, respectively. Metabolic imaging has the potential for early disease detection and therapy monitoring on an individualized basis. Metabolic imaging may be accomplished by positron emission tomography [PET], magnetic resonance spectroscopic imaging [MRSI], and with some effort also by single photon emission computed tomography [SPECT]. However, various problems arise with such approaches and improvements are sought. For example, the PET and HP-13CMRSI modalities are costly. Typical nominal spatial resolutions and voxel volumes for the human metabolic imaging modalities are: 31PMRSI [(1.3 cm)3=2.2 mL]; SPECT [(1 cm)3=1 mL], HP-13CMRSI [(7 mm)3=340 μL]; PET [(5 mm)3=125 μL]; and 23NaMRSI [(4 mm)3=64 μL] [see M. Inglese, G. Madelin, N. Oesingmann, J. S. Babb, W. Wu, B. Stoekel, J. Herbert, G. Johnson, “Brain Tissue Sodium Concentration in Multiple Sclerosis: A Sodium Imaging Study at 3 Tesla,” Brain 133, 847-857 (2010), hereby incorporated by reference herein in its entirety]. Such approaches are often insufficient for discriminating significant human anatomy. For example, the cerebral gray matter (GM)/white matter (WM) boundary usually cannot be distinguished. In comparison, MRI generated from the relatively strong 1H2O signal routinely offers substantially higher spatial resolution; (1 mm)3=1 μL, or better. Modern metabolic images are almost always accompanied by high-resolution MRI [and sometimes computed tomography (CT)] views of the same tissue. Understandably therefore, MRI is often thought of as providing only anatomical information with the exceptions of tissue function in some cases such as functional MRI and cine cardiovascular MR. Compared with PET and HP-13CMRSI, MRI is relatively inexpensive. Also, MRI employs no ionizing radiation.